举个例子 I like the book which I bought. book是先行词(就是定语从句修饰的那个词),which是关系代词(笼统的说也叫引导词,还有一类引导词是关系副词,比如when和where).连接词不一定用于引导从句,比如and和but,当然I think that he will come,这句宾语从句中,that作为连接词,也起了一个引导从句的作用. 语法练习及解析:http://wenku.baidu.com/view/e1155a1314791711cc791708.html